The zebrafish (Danio rerio) has become a unique vertebrate model for human disease research in hearing and balance because of a combination of powerful genetics, excellent embryology, and exceptional in vivo visualization in one organism. Recent studies use forward and reverse genetic manipulations and developmental approaches to generate a large variety of zebrafish hearing mutants in order to identify novel deafness genes and investigate auditory functions of target genes. However, auditory abilities of larval zebrafish are unknown due to lack of a method that can evaluate hearing function of zebrafish at early stages. This project has two specific aims. First, the PI will develop a reliable method that is suitable for determining auditory abilities of zebrafish larvae. There are two general ways (loudspeaker and shaker table) to produce acoustic stimuli that can activate sensory hair cells in the inner ear of fish. There are two common methods (auditory evoked potential recording and behavioral classical conditioning) to assess the auditory function of fish. The PI will investigate what setup and method are best suitable for determining auditory thresholds of young larval zebrafish. Results of this project will provide the zebrafish research community a hearing test that can precisely assess hearing defects of zebrafish mutants used for studying auditory disorders in humans. Second, the PI will investigate how the auditory function of wild-type zebrafish enhances during the early development after fertilization. The timeline of development of best frequency, best sensitivity, and audible frequency range will be determined for zebrafish of several different age groups from just hatching to adulthood. The PI will determine the critical period of development of hearing function and identify the time when the auditory capacities reach a plateau. We know little about what young larval zebrafish can hear and how their auditory function develops. Results from this study will fill this knowledge gap to further establish the zebrafish as a model system for auditory research. Easy accessibility of zebrafish embryos right after fertilization makes zebrafish an ideal candidate to investigate the early hearing development in vertebrates. Results from this study will help us better understand evolution of the early development of auditory function in vertebrates including humans. The method developed by this project will enable the zebrafish research community to precisely assess auditory functional defects of zebrafish mutants used for studying human hearing disorders and help further establish the zebrafish as a vertebrate model system for human hearing research. Results from this study will fill the knowledge gap of auditory abilities of larval zebrafish and provide insight into evolution of the early development of auditory function in vertebrates including humans.